Electron beam generating devices may be used in sterilization of items, such as for example in sterilization of food packages or medical equipment, or they may be used in curing of e.g. ink.
An electron beam generating device according to prior art is partly disclosed in FIGS. 1 and 2. The electron beam device 100 comprises two parts; a tube body 102 housing and protecting the assembly 103 generating and shaping the electron beam, and a flange 104 carrying components relating to the output of the electron beam, such as a window foil 106 and a support plate 108 preventing the window foil 106 from collapsing as vacuum is established inside the device 100. The support plate 108 should prevent the window foil 106 from collapsing while being transparent enough not to interfere with passing electrons. The copper support plate 108 further has an important purpose in conducting heat away from the foil, which otherwise would experience a shortened usable lifetime. The support plate 108 is attached to the flange 104, and the window foil 106 is welded onto the support plate 108 along a line (not shown) extending along the perimeter of the copper support 108.
Electrons are generated by the filament 110 and accelerated towards the window foil 106 by means of an applied voltage. On their way they pass a control grid 112 which may be given an electrical potential in order to control the electron beam.
As such, the maximum power output from the electron beam device is generally limited by the foil, since excessive powers will generally be limited by the durability of the foil. In a practical case the output current density will be distributed over the foil surface in what is referred to as the beam profile. The optimal beam would have a profile along an X-direction (shorter dimension of the window) as shown in FIG. 6 (dotted line) leading to a temperature distribution (dashed line) with a constant plateau region over the entire foil surface, in which case the level of the plateau region could reside on a level slightly above the level needed for sterilization. This is however rarely the case, and instead the beam profile follows a bimodal distribution (in the X-direction).